Amini has spent three seasons at the Bundesliga club but has been unable to break into the first-team during that time.
“I didn't expect this day to come so soon in my short lived career at BVB, but I thank you very much for an amazing 3 years I'll never forget,” Amini said on Instagram.
“The journey has made me learn a lot about myself and has turned me into a man that is ready for his next footballing challenge.
“After today a new journey will start for me where I'm now 22. It's important for me to try and fulfil my complete ability by playing first team football somewhere else.”
The 22-year-old recently ruled out a return to the Hyundai A-League, with his preference to stay in Europe.
It’s understood he has options to stay in Germany or move to either Belgium, the Netherlands or Denmark.
A photo posted by Mustafa Amini (@mustafaamini) on
If Amini can secure some consistent game-time next season he looms as a key figure for Aurelio Vidmar’s Olyroos as they look to qualify for next year’s Rio Olympics.